The mesic savannas of the Bateke Plateau: carbon stocks and ﬂoristic composition
, Edward T. A. Mitchard
, Roland Odende
, Marcelle A. Batsa Mouwembe
, Tim Rayden
Casey M. Ryan
School of GeoSciences, University of Edinburgh, Crew Building, Edinburgh EH9 3FF, UK
Laboratoire de botanique et d’
e des Sciences et Techniques, Universit
e Marien Ngouabi, BP 69, Brazzaville, Congo
Ecole Nationale Sup
erieure d’Agronomie et de Foresterie, Universit
e Marien Ngouabi, BP 69, Brazzaville, Congo
Wildlife Conservation Society, 2300 Southern Boulevard, Bronx, New York, USA
The Bateke Plateau in the Republic of Congo is one of the last frontiers for ecology, with little known about its ﬂoristics and physiog-
nomy. Despite occupying 89,800 km
and its importance for local livelihoods, its ecology and ecosystem functions are poorly under-
stood. Situated on Kalahari sands, the Bateke has a complex evolutionary history, mainly isolated from other savannas for much of its
past, with currently unresolved ecological implications. Here, we assess the biomass and ﬂoristic diversity of this savanna. We established
four 25-ha permanent sample plots at two savanna sites; inventoried all trees; assessed biomass and species composition of shrubs,
forbs and grasses; and characterized the soils. Total plant carbon stocks (aboveground and belowground) were only 6.5 0.3 MgC/ha,
despite precipitation of 1600 mm/yr. Over half the biomass was grass, with the remainder divided between trees and shrubs. The car-
bon stock of the system is mostly contained in the top layer of the soil (16.7 0.9 MgC/ha in 0–20 cm depth). We identiﬁed 49 plant
species (4 trees, 13 shrubs, 4 sedges, 17 forbs, and 11 grass species), with an average species richness of 23 per plot. There is tree
hyperdominance of Hymenocardia acida (Phyllanthaceae) and a richer herbaceous species composition dominated by Loudetia simplex and
Hyparrhenia diplandra. The low carbon stocks and tree biodiversity, compared to other African savannas, are surprising considering the
high rainfall. We speculate it is due to low nutrient soils, high ﬁre frequency, and the effect of a temporally variable and restricted con-
nection to the main southern African savanna complex.
Abstract in French is available with online material.
Key words: Bateke Plateau; carbon stocks; Republic of Congo; savanna; species composition.
THE BATEKE PLATEAU IS A SAVANNA-COVERED PLATEAU LOCATED
MAINLY IN THE SOUTHERN REPUBLIC OF CONGO, but also extending
into the east of Gabon and the southwest of Democratic Repub-
lic of Congo (DRC), and with an area of approximately
(Fig. 1). It comprises ﬁve different savanna plateaus
(Koukouya, Djambala, Nsa, Ngo, and Mbe/Bateke), with an eleva-
tion that ranges from 259 to 872 m (mean of 545 m), each sepa-
rated by deep valleys (Descoigns 1960, Congo Basin Forest
Partnership, 2006). The landscape is located on the northern part
of the Kalahari sands, an ancient sand dune system (Haddon
2000), with soils that are mainly deep, sandy in texture and ferralitic
(Schwartz & Namri 2002), providing rapid drainage. There are also
some podzols in lower areas (Schwartz 1988). This area has a tropi-
cal transitional climate, characterized by an average annual rainfall
of 1500–1800 mm (obtained from Harris et al. 2014). There is a
main dry season from June to September and a short dry season in
January and February (Walters 2010b). The Bateke Plateau has his-
torically low human population densities, around 0.2 inhabitants/
km²(Congo basin forest partnership 2006). Bateke populations
mainly practice subsistence agriculture, gathering, ﬁshing, and hunt-
ing (Walters 2010a, Rayden et al. 2014). Agro-economic activities,
charcoal production, logging, hunting, and bushﬁres have widely
impacted this landscape, driven by the demand from the large capi-
tal cities of Brazzaville and Kinshasa (populations of 1.8 and 9.5
million, respectively) (Hoare 2007).
The vegetation of the Bateke Plateau is predominantly a
mosaic of woody savanna and grasslands, with patches of closed
canopy forest, the latter conﬁned to rivers and valley ﬂoors,
pockets at the top of hills, and surrounding settlements, where
there is greater water availability and protection from ﬁre (Duvi-
gneaud 1953b). The wooded savanna is dominated by an open
canopy of Hymenocardia acida Tul. (Phyllanthaceae) and Annona
senegalensis Pers. (Annonaceae) trees, with an understory of grasses
and locally endemic forbs (Walters 2012). The grasslands are typi-
cally dominated by Loudetia simplex and Hyparrhenia diplandra
The Bateke Plateau intrudes into the Congo Basin rainforest
and has a precipitation clearly suitable for closed canopy forest
establishment. Here, savanna and forest coexist under the same
Received 24 May 2018; revision accepted 26 July 2018.
Corresponding author; e-mail: firstname.lastname@example.org
ª2018 The Authors. Biotropica published by Wiley Periodicals, Inc. on behalf of Association for Tropical Biology and Conservation 1
This is an open access article under the terms of the Creative Commons Attribution License, which permits use,
distribution and reproduction in any medium, provided the original work is properly cited.
BIOTROPICA 0(0): 1–13 2018 10.1111/btp.12606
climatic and edaphic conditions with sharp transitions (Schwartz
et al. 1995). This has made it problematic to deﬁne the origin of
this savanna, with conﬂicting hypotheses as to the lack of tree
cover, which have important consequences for its conservation
(Veldman et al. 2014, 2015, Bond & Zaloumis 2016). Some
authors (Aubreville 1949, Duvigneaud 1953b, Elenga et al. 1994)
have suggested an anthropogenic origin, caused by the arrival of
human populations. Conversely, the weight of recent evidence
supports an origin caused by arid events in the past, though
humans could have played a role (Koechlin 1960, Aubreville
1962, Foresta 1990, Elenga et al. 1994, Schwartz et al. 1995, Vin-
cens et al. 1999, Oslisly et al. 2013). The recent climatic history of
the region is complex. There is evidence of a humid period with
mainly forests covering the region from 40,000 to 24,000 years
BP, followed by a drier period from 24,000 to 12,000 years BP
when herbaceous communities expanded (Dechamps et al. 1988,
Schwartz 1988, Elenga et al. 1994, Schwartz et al. 1995). From
12,000 years BP onwards, humid conditions encouraged new for-
est development (Dechamps et al. 1988, Elenga et al. 1994),
supported by studies suggesting that, as recently as 4000-
3500 years BP, the Bateke Plateau was forested (Dechamps et al.
1988, Schwartz et al. 1995, Vincens et al. 1999). These forests
were likely replaced by open grasslands around 3000 years BP,
when a major arid event occurred with greater seasonality, caus-
ing extension of grasses (Elenga et al. 1994, Schwartz et al. 1995,
Vincens et al. 1999, Maley 2001), and coincident with the arrival
of increased human populations (Schwartz 1992). However, even
during the most humid episodes of the past 40,000 years, there
is evidence that some savanna still existed in the area (Dechamps
et al. 1988, Vincens et al. 1999).
The Bateke belongs to the Guineo-Congolian center of
endemism (White 1983), with most of the Bateke being in the
Western Congolian forest–savanna mosaic ecoregion (Olson et al.
2001). These savannas have been fairly isolated from other
savanna formations, especially from West Africa by the Congo
Basin rainforest. In the Guineo-Congolian region (White 1979)
and in southern Kalahari areas, endemism is high (Walters et al.
2006), with many sand-adapted and pyrophytic species. This
FIGURE 1. Map of the study area, the Bateke Plateau, located mainly in the Republic of Congo. The left-hand map shows the extent of the Bateke Plateau
(red), the Kalahari sands (dashed), and the weather station of Gamboma used for the analysis of the temperature and precipitation data (yellow dot). The right-
hand panel shows the location of the Leﬁni and Lesio Louna reserves, where the sampling plots were placed (red dots), over a Digital Elevation Model (DEM)
and the land use cover (GlobCover 2009, reclassiﬁed).
2 Nieto-Quintano, et al.
suggests potential for endemism in the Bateke, and indeed this is
supported by recent ﬁndings (Bamps 2013). In Gabon, there
have been recent reports of more than 30 new plant records
from savannas, and six globally rare species restricted to Kalahari
sands or moist savannas (Walters et al. 2006, van der Maesen &
Walters 2011), and in South Congo, Koechlin (1960) found 12%
endemic species. However, Bateke savannas were considered by
White (1983) as secondary with some being edaphic and by
Schwartz et al. (1995) as inclusive or edaphic, and original, with-
out equivalent in the past. The theory of Bateke savannas being
secondary would contradict potential endemism, as secondary
savannas tend to have lower plant species richness and absence
of geoxylic suffrutices (Zaloumis & Bond 2016). Plant species
with a geoxylic suffrutex growth form are plants with large
woody underground structures and short-lived aerial shoots, with
a high capacity to resprout stimulated by ﬁre, thus providing an
alternative escape from ﬁre (White 1977). They are mainly ende-
mic to the Kalahari sands of the Zambezian region and occur
almost exclusively in higher rainfall savannas with frequent ﬁres
(White 1977, 1979, Revermann et al. 2017).
There is evidence from charcoal that ﬁres have occurred in
the Bateke since 2100 BP, and almost certainly they occurred fre-
quently far further back in time (Schwartz 1988, Walters 2012).
Nowadays, ﬁres are mostly anthropogenic, occurring mainly in
the dry season for hunting and gathering (Walters 2010a, 2012).
Frequent ﬁres, fueled by the continuous layer of grasses, have
unclear effects on species richness (Higgins et al. 2000, Smith
et al. 2013) and probably encourage specialization (Walters et al.
2006). Herbivore densities are low and do not cause much distur-
bance due to historic and current hunting, though there probably
were once high herbivore densities that could have shaped the
landscape (Walters 2010b).
BIOMASS STOCKS AND BOTANICAL STUDIES INTHE BATEKE
PLATEAU.—Savannas cover around half of the African continent
(Menaut 1983), but despite their importance to the global carbon
cycle, current knowledge of African savanna biomass stocks and
ﬂoristic diversity is limited (Hall & Scurlock 1991), especially in
the understudied ecosystems of the Bateke Plateau.
We searched and collated the published and gray literature
of the Bateke to provide a ﬁrst comprehensive review of the bio-
mass stocks in the Plateau and found eight studies that have pre-
viously quantiﬁed some aspects of biomass stocks of these
savannas (Makany 1973, Apani 1990, Schwartz & Namri 2002,
Yoka et al. 2010, 2013, Gigaud 2012, Lokegna 2015, Ifo 2017).
These values are in general low for African savannas. There have
been still fewer estimates of soil carbon stocks in the Bateke Pla-
teau (Namri 1996, Schwartz & Namri 2002, Ifo 2017). The spa-
tial scale of all these studies is restricted, and none have assessed
all ecosystem carbon storage elements together, limiting their abil-
ity to provide understanding of the system.
We have better knowledge of the plant species of the region,
with ﬂoristic inventories of Gabon (Aubreville 1961) and DRC
(Robyns 1949), and a Checklist for Gabon (Sosef 2006). In RoC,
there is a published inventory for the vascular ﬂora of the Republic
of Congo (Sita and Moutsambote (1988)), which provides a list of
4397 species (198 families and 1338 genera), but with the vast
majority being forest species and no indication of their distribution.
This inventory has been slightly updated since then, with 84 species
added by Champluvier and Dowsett-Lemaire (1999), and 64 by
Lachenaud (2009). More usefully, there is an illustrated list of plants
of the Lesio Louna and Leﬁni reserves, which are major reserves
covering 6% of the Bateke Plateau, that list 457 species belonging
to 119 families (Nsongola et al. 2006). Some old botanical studies
in French of this landscape also exist, but they are limited to the
South of the Bateke (Koechlin 1960, Descoigns 1972), the Cuvette
region (Descoigns 1960, Yoka et al. 2013), and the Teke Plateau
(Makany 1973, Apani 1990), and in more recent some masters’the-
ses (Lokegna 2015, Mampouya 2015). However, all these studies
are limited in scope, contributing to the Republic of Congo being
one of the botanically least known and inventoried countries in
tropical Africa (Lachenaud 2009, Sosef et al. 2017).
Due to the lack of basic data on this ecosystem, it is difﬁcult
to understand its function, conservation value, and the transfor-
mations it could undergo with climate change and management
changes. Our main objective was to characterize the structure of
the vegetation and ﬂoristic diversity of the Bateke Plateau using
data collected from four very large (25-ha) inventory plots,
located within two protected areas and designed as a long-term
ﬁre experiment. Our research questions were as follows: (1) What
is the carbon storage of our two woody savanna study sites, and
how is it distributed between vegetation and the soil? (2) What is
the species diversity of the study sites, and how does diversity
vary by plant life form type? (3) Can we explain the structure of
these savannas in the context its biogeographical history and
Due to frequent ﬁres and intermediate rainfall, we expected
these savannas to have a low tree biomass but higher grass bio-
mass and understory diversity, with the presence of pyrophytes
and geoxylic suffrutex species. Moreover, if these savannas are
ancient as recent evidence suggest, with a ﬂuctuating savanna/
forest cover for at least past 40,000 years, and because of its geo-
graphical position, we would anticipate high plant and forb diver-
sity, presence of geoxylic suffrutex, and some endemism. We
would expect ﬂoristic similarities with the southern savannas due
to the Kalahari sands acting as a corridor.
Overall, we provide a baseline biomass and diversity inven-
tory for these savannas that we hope will be useful to other sci-
entists interested in their structure and function, and assist with
their management and conservation.
SITE DESCRIPTION.—We conducted the study in two protected areas
in the Bateke Plateau, the Leﬁni and the Lesio Louna reserves
(Fig. 1), situated about 160 and 110 km north of Brazzaville,
respectively. These sites have a precipitation of 1627 to 1966 mm/
yr and a mean annual temperature of approximately 25°C (all cal-
culated for the period 1996–2016 from data of Climate Research
Unit (CRU) for the station of Gamboma (Harris et al. 2014), see
Carbon and Floristics of the Bateke Plateau 3
Fig. 1 for location). The Leﬁni Wildlife Reserve (LWR) has a total
area of 5010 km
(IUCN & UNEP 2015) and was established in
1951 as a hunting reserve. The Lesio Louna Reserve (LLR) has a
total area of 1730 km
and was established in 1993 as a sanctuary
for the reintroduction of orphan gorillas by the Aspinall Founda-
tion and later as a Natural Reserve in 1999. Both reserves are listed
as IUCN Category IV and aim to maintain, conserve, and restore
species and habitat (IUCN & UNEP 2015). They feature typical
Bateke habitats: rolling hills studding a plateau dissected by river
valleys, with open savanna dominating, and with forest patches
around rivers and on the top of hills.
CARBON STOCK ASSESSMENT.—We established four 25-ha perma-
nent sample plots (500 m 9500 m) in the savanna, two in each
protected area, in the year 2015 as part of a long-term ﬁre exper-
iment (plots LWR1 and LWR2 in Leﬁni and plots LLR1 and
LLR2 in Lesio Louna). The plots were not randomly located,
selected to be in wooded savanna, easily reachable by foot from
research camps, and sufﬁciently large to encompass much of the
natural variability of the savannas. All four plots were located
with one edge running about 30 m away from the edge of closed
canopy forest, associated with nearby rivers. Data collection took
place in 2015 in the beginning of the dry season (May/June) for
plots LWR2 and LLR1 and in the end of the dry season
(September/October) for plots LWR1 and LLR2.
In these plots, we inventoried all living trees with a diameter
at breast height (dbh) greater than 10 cm, recording: species,
dbh, height, status (alive/dead, standing/fallen, and broken), and
spatial location (by GPS). Dbh was measured at 1.3 m height
aboveground, and if the tree forked below this, each stem was
measured independently and treated as different trees. Trees were
identiﬁed to species level by Roland Odende, and their height
was estimated using a Nikon Forestry Pro Laser.
For the estimation of the aboveground biomass (AGB) from
these measurements, we used the generic pan-tropical allometric
equation from Chave et al., (2014) with wood density obtained
from the Wood Density Database (Chave et al. 2009, Zanne et al.
2009) based on the species determination. This was considered
the most appropriate for the study site as there are no locally
deﬁned allometric equations for this location. As height was esti-
mated individually on the ground for every tree, there was no
need to use diameter measurements to estimate tree height
through a locally derived or regional relationship. However, we
did compare dbh and height values in order to test the strength
of this relationship in this ecosystem and to develop a model for
use by others. Belowground tree biomass (BGB) was not mea-
sured in the ﬁeld, but estimated using a root-to-shoot ratio
(R:S =0.42) described by Ryan et al. (2011) for miombo woodlands.
We consider this equation was appropriate as the trees are subject to
similar ecological pressure and constraints, and due to the absence of
a local equation or one for Central African savannas.
To survey grasses and saplings/shrubs, the latter deﬁned as
woody plants with a dbh <10 cm and with a diameter at 10 cm
) greater than 1 cm, 16 permanent circular
subplots with a radius of 4 m (50.3 m
) were established within
each plot, on every 100 m vertex, as shown in Fig. 2. In these
subplots, saplings were tagged; measured (D
) using a calliper,
height, and dbh where applicable; and identiﬁed to species level.
To estimate the biomass of the saplings (stems and roots), the
allometric equations from Ryan et al. (2011) were applied for sap-
lings with dbh <5 cm.
SBs ¼0:0007645 D102þ0:004645 D10 þ0:03876 (1)
SBr ¼0:001784 D102þ0:0001413 D10 þ0:15839 (2)
where, SBs and SBr is the stem and root wet sapling biomass in
kg, respectively. This was converted to biomass Mg/ha using the
dry mass fraction (DMF) of 0.61 determined in the same study.
For saplings with D
≥5 cm and dbh <10 cm, the Chave et al.
(2014) Equation 1 was used for the AGB, and the ratio R:
S=0.42 for roots.
Grass biomass was measured using a disc pasture meter
(DPM) (Bransby & Tainton 1977, D€orgeloh 2002), by taking four
measurements at each subplot (therefore 64 measurements per
25-ha plot). The DPM was calibrated in each plot before its use. In
order to perform this calibration, all the grass under the DPM was
cut and weighed (wet weight). A subsample of grass was weighed,
then dried to the point of no further weight loss, and re-weighed in
order to determine dry mass based on percentage moisture loss
from the samples. The relationship between mean disc settling
heights (cm) and grass biomass per quadrat was determined sepa-
rately for each plot using linear regression (linear calibration curve,
N=35–40 for each plot, r
=0.35–0.75). BGB was not measured
in the ﬁeld, but it was estimated using the ratio calculated by Apani
(1990) for grasses in the Teke Plateau (R:S =2.5).
Biomass was converted into carbon stocks using a conver-
sion factor of 0.47 (Ryan et al. 2011) for woody plants and 0.42
for grasses (Ryan 2009). All biomass values are given in metric
tonnes of carbon per ha (MgC/ha).
SOIL ANALYSIS.—Soil analysis was performed in Plot LWR2
(Leﬁni) and LLR1 (Lesio Louna), by taking two soil samples
(4 m apart) in each subplot located in the transects numbered 2
and 4 (Fig. 2), at two different horizons, h0 (0–5 cm) and h1 (5–
20 cm), giving 32 soils samples per plot. Samples were dried,
sieved, and analyzed in the physiochemical laboratory of the
Institut de Recherche en Sciences Exactes et Naturelles (IRSEN)
at Pointe-Noire, in order to determine total organic carbon, nitro-
gen content, and bulk density (measured with a cylinder core to
assess the volume of the soil and determine the weight after dry-
ing, (Blake & Hartge 1986) (Batsa et al. (2017).
SPECIES COMPOSITION.—We performed a survey of the ﬂoristic
composition by identifying all plant species within the subplots
(presence/absence), ﬁrst in situ, and where not possible samples
were taken to the National Herbarium of IRSEN for identiﬁca-
tion, as described in Odende (2016). For six species, the identiﬁ-
cation was only possible to genus level. For the species
4 Nieto-Quintano, et al.
nomenclature, the Sita and Moutsambote (1988) ﬂora inventory
and the Plant list data base (The Plant List, 2013) were used.
Species were further categorized into the different life forms
(trees, shrubs, sedges, forbs, and grasses). To further categorize
shrubs and trees as geoxylic suffrutex, we used the deﬁnition of
White (1977) as plants with a ‘massive, woody, underground axes
but only annual or short-lived shoots aboveground’, and use the
list provided in (Maurin et al. 2014). Species diversity was calcu-
lated using species richness for all presence/absence data, as the
total number of unique species observed in each subplot.
DATA ANALYSIS.—We investigated the within-plot variances using
linear models and one-way analysis of variance (ANOVA). To
evaluate to what extent species were well sampled, we con-
structed rareﬁed species accumulation curves. Dissimilarity in
species composition between sites (beta diversity) was calculated
using Sørensen dissimilarity index. Compositional patterns were
visualized using a non-metric multidimensional scaling (NMDS),
and correlations between the ﬂoristic composition and environ-
mental characteristics were assessed with multiple regression, by
ﬁtting the ecological variables to ordination scores using the ‘en-
vﬁt’function of the vegan package (Oksanen et al. 2013).
All data analyses were performed using the R statistical soft-
ware v. 3.1.3 (R Core Team, 2015, http://cran.r-project.org),
using the vegan (Oksanen et al. 2013), spatstat (Baddeley &
Turner 2005), pgirmess (Giraudoux 2017), and iNEXT (Hsieh
et al. 2016) packages.
BIOMASS STOCKS.—In total, we inventoried 4120 live tree stems
with a dbh ≥10 cm in our 100 hectares ﬁeld plots
(LWR1 =726, LWR2 =1480, LLR1 =1022, and LLR2 =892),
with a maximum dbh of 39.3 cm. The tree, grass, and saplings/
shrubs carbon stocks on a plot basis are summarized in Table 1,
with a mean total of 6.47 0.33 MgC/ha. Grass carbon stocks
were in general about equal to that of tree, shrub, and sapling
biomass combined, though there was considerable variation both
within and between plots. Plots had signiﬁcantly different above-
ground biomass for trees (ANOVA single factor, P<0.05) and
Approximately 90% of the tree AGB was stored in trees
with a dbh between 10 and 22 cm, with large stems rare (Supple-
mentary Information Fig. S1). The stem density of the plots var-
ied from 29.0 (plot LWR1) to 59.2 tree stems per hectare (plot
LWR2) (Fig. S2).
SOIL CARBON AND NITROGEN.—The mean bulk density of the 0–
20 cm horizon was 1.48 0.01 Mg/m
1.44 0.01 Mg/m
(LLR1) (soil analysis results summarized in
Table S1). Carbon stocks and the C:N ratio were very low
in both sites. Soil carbon content estimations were very similar in
both proﬁles, being slightly higher in the h0 proﬁle than in the
h1, with an average of 16.74 MgC/ha. Carbon stocks and C:N
ratios were not signiﬁcantly different between sites (ANOVA sin-
gle factor, P>0.05).
We also found that dbh was a predictor of tree height,
although with a weak positive relation (R
=0.14, P<0.001) in
all plots (see Fig. S3 for graph and equation). Ninety percent of
the inventoried trees with a dbh ≥10 cm were taller than 3.1 m.
SPECIES CHARACTERIZATION.—We identiﬁed 49 species in total (4
trees, 13 shrubs, 4 sedges, 17 forbs, and 11 grass species). A
complete list of the species is given in the Supplementary Infor-
mation (Table S2). For trees, Hymenocardia acida Tul. (Phyllan-
thaceae) was hyperdominant, comprising 93.8% of the
FIGURE 2. Sampling method. Plots were 500 9500 m (25 ha), with subplots placed every 100 m. Each subplot had a radius of 4 m in which grass and soil
(transects 2 and 4 only) measurements were taken.
Carbon and Floristics of the Bateke Plateau 5
inventoried stems across all plots (Table S3 in Supplementary
Information). There were 27 species common to both sites, 3
unique to Leﬁni, and 11 unique to Lesio Louna. The Sørensen
index of dissimilarity between the two sites was 0.21, which indi-
cates a 21% dissimilar species composition between sites. The
most abundant grass species in all subplots was Loudetia simplex
and Hyparrhenia diplandra. Poaceae was the dominant family across
the plots, followed by Fabaceae and Cyperaceae. Fig. 3A summa-
rizes the number of species per plot divided into vegetation types.
Species richness was similar for all plots (LWR1 22, LWR2 25,
LLR1 29, and LLR2 23), with a mean of 25 3. There is a high
presence of woody species with a geoxylic suffrutex growth form
(Table S2), and the understory is more diverse.
The rareﬁed species accumulation curves (Fig. 3B) are com-
parable among the plots. The estimated sample completeness was
for plot LWR1 96%, LWR2 99%, LLR1 93%, and LLR2 97%.
When comparing diversity at the subplot level, NMDS ordination
showed dissimilarity of the two sites in relation with the species
composition of the subplots, but little difference between the two
plots within each site (Fig. 4). Variation in species composition is
best explained by the distance to forest, elevation, and tree and
grass aboveground biomass (NMDS, P<0.05).
CARBON STOCKS AND COMPARISON WITH OTHER STUDIES.—At our
two sites, the average total vegetation carbon stocks (above-
ground and belowground) was 6.5 MgC/ha, with the topsoil
horizon (0–20 cm) holding over twice as much, 16.8 MgC/ha
(Fig. 5, and considerably more carbon likely stored at deeper
depths not investigated here).
The climate of the Bateke Plateau, with annual rainfall of
~1600 mm and an intense 3–4-month dry season, would suggest
a closed canopy forest in the absence of disturbances (Sankaran
et al. 2005). Tree cover generally increases with rainfall, but ﬁre is
an important disturbance in areas with intermediate precipitation
(Staver et al. 2011). On Kalahari sands, there is also a gradient of
increasing woody cover and biomass with increasing precipitation,
at least in the southern section (Scholes et al. 2002). Conse-
quently, although we would expect the Bateke to have a high
woody cover and tree density, the observed low biomass could
be the product of frequent ﬁres, which reduce woody cover and
maintain the grasslands (Favier et al. 2004, Staver et al. 2011),
and the sandy soils, which are poor in organic matter and nutri-
ents (Yoka et al. 2010) and have a high percolation rate. The high
precipitation favors grass productivity, providing more fuel for
ﬁres. Savannas with sandy nutrient-poor soils are more likely to
favor woody over herbaceous cover (Scholes 1990, Sankaran et al.
2005, Bond 2008), although the edaphic conditions can also be a
restriction for trees (Mills et al. 2013). Tree seedlings compete
with grasses for water and nutrients belowground (Scholes &
Archer 1997), but disturbances are the main determinants for
trees not attaining the maximum woody cover established by
water availability (Mills et al. 2013).
Although these carbon stock values appear low for savannas,
they are not unusual for the Bateke (Table 2). The tree biomass
estimated in this study is between the values obtained by Apani
(1990) for the Teke Plateau and by Gigaud (2012) for the DRC.
Grass biomass is also similar to that calculated by Yoka et al.
(2013) for the South of RoC and to Makany (1973), but is lower
than some other studies (Apani 1990, Yoka et al. 2010). This
could be due to the timing of the sample collection, which were
later in the year than the likely time of maximal grass biomass,
around May at the end of the main wet season (Apani 1990,
Yoka et al. 2010). In the Kalahari sands, Scholes et al. (2002)
found that grass biomass increased with higher precipitation up
to 600 mm and then decreased due to competition with trees (up
to 1000 mm). This does not appear to be the case in our two
TABLE 1. Summary of the average carbon stocks per hectare (MgC/ha). For grasses and saplings/shrubs, indicates the standard error per plot of 16 950.3 m
subplots; and for
tree stems, it is the standard error of 25 91 ha subplots.
Biomass stock (MgC/ha)
MeanLWR1 LWR2 LLR1 LLR2
Stems 0.67 0.11 2.26 0.09 1.39 0.07 0.58 0.04 1.22 0.09
Roots 1.69 0.27 5.65 0.23 3.47 0.16 1.45 0.09 3.06 0.23
Grasses Total 2.34 0.29 7.91 0.25 4.86 0.18 2.03 0.10 4.28 0.25
Stems 0.52 0.13 0.66 0.34 0.64 0.28 0.26 0.10 0.52 0.12
Roots 0.86 0.44 0.57 0.52 0.71 0.70 0.53 0.28 0.63 0.13
Saplings Total 1.38 0.24 1.23 0.42 1.36 0.43 0.79 0.30 1.15 0.18
Stems 0.42 0.09 1.01 0.11 0.77 0.16 0.68 0.07 0.74 0.06
Roots 0.18 0.04 0.42 0.05 0.32 0.07 0.24 0.03 0.29 0.02
Trees Total 0.60 0.10 1.42 0.12 1.10 0.17 0.92 0.07 1.03 0.07
Total 4.33 0.41 10.57 0.52 7.31 0.51 3.74 0.32 6.47 0.33
6 Nieto-Quintano, et al.
sites, but further research about tree–grass competition is needed
to better understand this system.
The biomass of saplings/shrubs was higher than might be
expected from a visual assessment, which suggests a landscape
dominated by grass and scattered trees. The density of shrubs in
this landscape was very patchy, and the subplot density measure-
ments have a non-normal, right-skewed distribution, with many
plots not having any shrubs, and some containing high densities.
Larger or more subplots would be required for a more robust
shrub biomass estimation.
FIGURE 3. (A) Number of species per plot by type (trees, shrubs, sedges, forbs, or grasses) and total. (B) Rareﬁed species richness showing the cumulative num-
ber of species observed and an extrapolated sampling curve (dashed line) of subplot species for all plots (N =16 subplots per plot) and for all combined
FIGURE 4. Non-metric multidimensional scaling (NMDS) ordination for all the ﬂoristic data (grass and woody plants). Big circles grouping the sites (Lesio
Louna [LLR] and Leﬁni [LWR]), ﬁll circles grouping the subplots (LWR1, LWR 2, LLR1, and LLR2), with conﬁdence limit for ellipses of. 0.95. Floristic composi-
tion was correlated with environmental vectors, displayed as arrows (where P <0.05, and *where P <0.01). Elevation (m) =elevation relative to lowest point in
Carbon and Floristics of the Bateke Plateau 7
Few studies have quantiﬁed the BGB in the Bateke, but our
results are similar to those obtained by Apani (1990) for grasses
and Lokegna (2015) for trees. These values (mean) are low
compared to reported general tropical savannas root biomass,
such as the 6.48 MgC/ha reported by Jackson et al. (1996) for
tropical grassland savannas. Tree, shrub, and grass BGB were
estimated with ratios found in the literature, and therefore, having
local allometric equations would provide better estimates. More-
over, we might have underestimated by using the mean root-to-
shoot ratio described by Ryan et al. (2011), as this ratio varied
from 0.27 to 0.58. The BGB of the geoxylic suffrutex species will
have been underestimated as they contain disproportionately large
Our savanna plots were characterized by a very low tree
stem density (averaging 41.2 stems per ha) and low biomass, con-
sistent with systems with high disturbance. This result indicates
the importance of using large (>10 ha) plot areas for the inven-
tory of this biome, as savannas are highly heterogeneous. How-
ever, in order to capture all landscape variability, larger scales of
sampling would be needed (Staver 2017).
The topsoil contributes the most to the carbon pool in our
plots (16.7 MgC/ha, 53% of the total), in concordance with other
studies of savannas (Scurlock & Hall 1998, Ciais et al. 2011), and
the low carbon density of these soils is similar to other studies in
Kalahari sands (Bird et al. 2004). Soil carbon stocks are similar to
those found in other studies of the Bateke Plateau (Table 2), such
as Ifo (2017), and slightly lower than Schwartz and Namri
(2002). Additionally, these values are much lower than in miombo
woodlands, where the median soil C stocks (0–30 cm) were 35.9
tC/ha, but supporting a much higher aboveground woody bio-
mass of 28.7 tC/ha (Ryan et al. 2016). Carbon content estima-
tions were very similar in both proﬁles, being slightly higher in
the h0 proﬁle than in h1. These carbon stock estimations are
important for further studies, to inform conservation measures
and in the design of more effective data collection protocols.
SPECIES DIVERSITY AND COMMUNITY COMPOSITION.—The ﬂoristic
inventory results are in concordance with those of other authors
for the Bateke (Duvigneaud (1953a), Makany (1973) and Nson-
gola et al. (2006)). Most of the tree species inventoried are typical
of dry savannas (Duvigneaud 1949). Many authors in fact
denominate this type of savanna of the Bateke as Hymenocardia
savanna (Duvigneaud 1953a, Descoigns 1972, Makany 1973),
dominated by Hyparrhenia diplandra or by L. simplex (e.g., Makany
1973, Walters et al. 2013). H. acida, is a deciduous, ﬁre-tolerant
(Trapnell 1959), small tree that occurs in tropical African savan-
nas mainly on sandy, loamy, or clayey soils (Duvigneaud 1949). It
reproduces asexually through production of resprouts, stimulated
by frequent ﬁres (Walters 2012). Koechlin (1960) described that
he never saw a H. acida seedling in the area, which implies the
FIGURE 5. Representation of the average carbon stocks (MgC per hectare) for all the plots in the study sites. Soil is Soil Organic Carbon (SOC) stock.
8 Nieto-Quintano, et al.
importance of vegetative reproduction (Walters 2007). Boaler and
Sciwale (1966) found for miombo woodlands that H. acida was
one of the fastest growing trees, therefore potentially making
them grow quickly enough to escape mortality by ﬁre in places
given enough precipitation, like in the Bateke. These characteris-
tics of H. acida could explain its hyperdominance in this system.
In our inventory, we found six shrubs and trees with a
geoxylic suffrutex growth form (Table S1), indicating a pyro-
phytic component of the ﬂora and potentially an established
savanna in a climate suitable for forests (White 1977, Walters
et al. 2006, Maurin et al. 2014). We have also found some Cyper-
aceae species, which often occupy recently burned grasslands, and
some pyrophytes, including H. acida, A. senegalensis, Bridelia ferrug-
inea, Psorospermum febrifugum, and Maprounea africana (Walters et al.
2006), which highlights the importance of ﬁre in maintaining
these ecosystems. Fire is likely responsible for maintaining the
forest–savanna mosaic with abrupt boundaries between forest
and savanna areas. We did not ﬁnd savanna–forest transition spe-
cies found in similar habitats, like Walters et al. (2006) in Gabon,
perhaps indicating the savanna at our sites has been stable for
The species diversity we found is quite low compared to
other African savannas, for example in South Africa (Fynn et al.
2004, Smith et al. 2016) and for miombo woodlands (Masocha
et al. 2011). The species richness is more comparable to values
obtained for natural grasslands in South Africa, and greater than
those for any secondary grasslands (Zaloumis & Bond 2016),
suggesting these savannas are not new and probably have existed
as a mosaic for long time. We also did not ﬁnd any endemic spe-
cies in our inventory, with most of them having wider distribu-
tions in Africa. However, we only subsampled 100 ha of
savanna, from two sites located only 86 km apart, so our conclu-
sions about plant diversity cannot be assumed to apply to the
whole plateau. In Gabon, Wieringa and Sosef (2011) found for
the Bateke Plateau National Park a relatively unique ﬂora with a
limited spatial extent, and Walters et al. (2006) encountered more
endemism in forests than in savannas. Although the Bateke
belongs to the Guineo-Congolian regional center of endemism
(White 1983), some studies had found species distributions simi-
lar to other regions. Walters et al. (2006) concluded in their analy-
sis about ﬂoristics in the Gabon’s Bateke Plateau that over 50
percent of the species were classiﬁed as Guineo-Congolian, but
20 percent had extended distributions into the Zambezian or
Sudanian phytochoria, and that sites on Kalahari sands in Gabon
shared ﬂoristic afﬁnities with Leﬁni. Similarly, Koechlin (1960)
determined for the Kalahari sand savannas in the south of RoC
that 12% of the species were endemic and 55% had a Sudano-
Angolan distribution (Walters et al. 2006). Duvigneaud (1953a)
described the Kalahari plateau in the DRC (Kwango) as an inter-
mediate zone, with a Guineo-Congolaise climate but with Zam-
bezian elements due to the edaphic conditions. Additionally,
Fayolle et al. (2018) concluded, using the data presented here, that
Leﬁni and Lesio Louna have ﬂoristic similarities with Northern
and Western African savannas and woodlands. The mixed ﬂoris-
tic composition of the Bateke is likely due to its historical spatial
geography. These savannas have been fairly isolated from other
savanna formations, with only some exceptions. The ﬂoristic
afﬁnities with the south and east could be explained by a connec-
tion via a savanna corridor with the Angolan highlands (Fayolle
et al. 2018) and by the Kalahari sands sheets, which could have
provided a connection with southern species, although this
hypothesis remains uncertain (Walters et al. 2006). The similarities
with the northern savannas could be explained by the fragmenta-
tion of the Congo Basin forest during the Last Glacial Maximum
(18000 years ago) (Maley 1991, Fayolle et al. 2018). Furthermore,
the Sangha River Interval provided a large savanna corridor con-
necting the Sudanian savannas in the north to the Bateke savan-
nas (Maley 2001, Maley & Willis 2010, Bostoen et al. 2015).
TABLE 2. Allocation of carbon stocks (MgC/ha) in the Bateke Plateau savannas from different studies.
Grasses (MgC/ha) Trees (MgC/ha)
Soil (MgC/ha) AreaRoots Stems Roots Stems
Makany (1973) 1.39
Plateaux Teke RoC
Apani (1990) 4.31 1.78 0.17
Plateaux Teke RoC
Gigaud (2012) 1.66
Lokegna (2015) 1.85
Bateke (Mah) RoC
Yoka et al. (2010) 1.72
Yoka et al. (2013) 1.18
Schwartz and Namri (2002) 15–20 (0–10 cm)
86–102 (0–100 cm)
Ifo (2017) 13.28 (0–20 cm)
45.95 (0–100 cm)
Lesio Louna RoC
This study 3.06 0.23 1.22 0.09 0.29 0.02 0.74 0.06 16.74 0.9 (0–20 cm) Leﬁni/Lesio Louna RoC
Trees and shrubs.
Average of the Bateke land unit.
Carbon and Floristics of the Bateke Plateau 9
Our results show that the Bateke savannas store only small quan-
tities of carbon per hectare, with the largest pools in the soil and
roots. Its species diversity is low, and we found no evidence of
endemism. The savanna ecosystem is clearly controlled by ﬁre,
with all plants showing adaption to regular burning. We have fur-
ther shown the need to use large plots (>10 ha) to capture varia-
tions in carbon stocks and species diversity in this area. These
data will thus inform future studies on optimal sampling method-
ologies and carbon dynamics in this ecosystem. Our results,
although only representative of part of the Bateke, will further
help in understanding the complex relationship between grasses,
understory plants, trees, ﬁre, and resources. However, more stud-
ies are needed in this ecosystem to inform conservation and
restoration, particularly with regard to ﬁre regime, and to under-
stand future challenges from climate change.
Funding for this work was provided by the US Forest Service
(USFS) and the University of Edinburgh. We thank USFS and
Wildlife Conservation Society-Congo (WCS) for providing logis-
tics and institutional support. We thank numerous ﬁeld assistants
(Roland Odende, Marcelle Armande Batsa Mouwembe, Ledia
Bidounga, and Onesi Samba) and ecoguards of Leﬁni and Ibou
Briko, Prime Mobie and Denis Ngatse, for their invaluable help
and knowledge; Mr. Gilbert Nsongola for helping with the spe-
cies identiﬁcation; and the people of Mpoh and M^ah for main-
taining the ﬁrebreaks and for sharing their knowledge about ﬁre
use. Edward T. A. Mitchard and Casey M. Ryan were supported
by the NERC-funded Socio-Ecological Observatory for the
Southern African Woodlands (NE/P008755/1).
Data used in this study are archived at the Dryad Digital Reposi-
tory: doi.org/10.5061/dryad.2122768 (Nieto-Quintano et al. 2018).
Information on using the vegetation data prior to the end of the
embargo can be found at seosaw.github.io.
Additional supporting information may be found online in the
Supporting Information section at the end of the article.
TABLE S1. Soil characteristics of Leﬁni and Lesio Louna.
TABLE S2. Species composition list (presence/absence data) for all
TABLE S3. Stem species number per plot for all trees.
FIGURE S1. AGB and cumulative sum of AGB vs. dbh
classes for all plots for trees.
FIGURE S2. Density of stems per hectare for all plots, with
box and whisker data based on individual values for the
25 91 ha subplots within each 25 ha plot.
FIGURE S3. Dbh vs Height for all trees in all plots, with
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